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Concave Reamer Blades

Publishing Venue

The IP.com Prior Art Database

Abstract

State of the art reamer blades for downhole tools feature a straight or convex drilling structure. This invention features a concave reamer blade design. The advantages of the new design will be: less torque generated, less risks of back-offs, less lateral and torsional vibrations, higher weight on reamer (WOR) capability. Furthermore Depth of cut (DOC) control measures can be applied with this new design, leading to an optimal aggressiveness of the blades, resulting in less stick slip.

Country

United States

Language

English (United States)

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Concave Reamer Blades

Abstract:

State of the art reamer blades for downhole tools feature a
straight or convex drilling structure. This invention features a concave reamer
blade design. The advantages of the new design will be: less torque generated,
less risks of back-offs, less lateral and torsional vibrations, higher weight
on reamer (WOR) capability. Furthermore Depth of cut (DOC) control measures can
be applied with this new design, leading to an optimal aggressiveness of the
blades, resulting in less stick slip.

Goal of this proposal is to overthink the actual reamer
blade design and aiming for a design which induces less vibrations and
increases drilling stability. Therefore a new design for reamer blades is
proposed as a foundation for this progress.

Description:

With reamers, there are two cutting structures in the
drillstring – reamer and bit. Both will induce drilling dynamics into the
drillstring. That’s why it is important to match those two drilling structures
together. But this is difficult.

State of the art bits have a lot of flat angle cutters and
just a few gauge cutters (outer most cutters). The reason for this is that the
flat angle cutters are able to take a lot of weight, while the gauge cutters
induce a lot of torque into the drillstring. Studies showed that “[…] long
profile/cone shaped bits are more prone to stick-slip” (Jain, et al., 2011).

State of the Art reamers have long blades with a lot of
gauge cutters. The reason behind this shape is, that the outer most part of a
bit was taken, scaled up to the desired size and loaded with cutters. These
cutters, mostly all of them, are placed on the gauge, which results in high
torque values during reaming. The blades are shown on the left side of the
following Figure 1,
the bit that was reviewed in (Jain, et al., 2011) on the right. The shape of the blades
of the unfavorable bit is looking nearly identical to the state of the art reamer
blades.

The past showed that there were some incidents where high
torque values on the reamer resulted in a stick slip of the reamer, while the
pilot BHA (BHA below the reamer) was spinning freely. The bit outdrilled the
reamer. Ultimately this lead to a back off of the drillstring below the reamer
because of its rotational inertia.

Too aggressive drilling structures are also more prone to
stick slip than less aggressive ones (Jain, et al., 2011). Knowing this, reamer blades should be
designed to be less prone to stick slip due to the below hanging pilot BHA that
can otherwise be backed off.

Furthermore new measurements showed that reamers induce high
lateral vibrations into a drillstring. The result during reaming looked like
shown in Figure 2
(vertical axis unit: [g]). Reducing those vibrations that are mainly a result
from the drilling structure would be beneficial for the whole reaming-service.